This invention relates generally to lenticular lenses and more particularly to thermoformed lenticular lens sheets.
The use of lenticular lenses in multiple image display devices is a well-established practice. Such display devices typically include a printed sheet or image panel having a composite image defined by interlaced image bands from two or more distinct images. A transparent sheet having a plurality of elongate, parallel lens elements, or lenticules, is placed over the printed sheet. The image bands are situated with respect to the lenticules such that the display device exhibits different images when viewed from different lines of sight. Multiple image display devices have been used in relatively small devices such as cards, buttons, pins and other novelties for many years. Attempts have been made to utilize lenticular display devices in larger displays such as billboards and the like. However, producing an array of lenticules large enough for such applications has proven to be a difficult and expensive endeavor.
Manufacture of lenticular lens sheets is currently accomplished through a variety of established methods including injection molding, compression molding, embossing, machining, extruding and casting. In addition to being unable to inexpensively form large lenticular lens sheets, these conventional methods are typically slow and expensive and often require large, complex machinery. Furthermore, they are not easily adapted to making lenticular lens sheets of different sizes and shapes.
Many lenticular lens sheets used in conventional display devices are designed to have lenticules with a distinct focal point or narrow focusing, typically with a focal length that is equal to the thickness of the lens sheet. That is, they strive to focus incident light rays from a given line of sight onto a single point. In this sense, the term "focus" refers to the phenomenon of a convex lens causing incident light rays to converge onto a focal point and does not refer to the sharpness or clarity of an image. Also, because of the elongate nature of these lenticules, incident light rays are focused into a line instead of a point, but the term "focal point" will be used herein to follow the common convention. Narrow focusing is desirable because it permits many images to be incorporated into the composite image, thereby providing a display device with a strong animation effect. However, narrow focusing also results in high magnification of the images with a corresponding washed out appearance. Narrow focusing also means that illumination light will be focused into narrow strips on the image bands. Consequently, the device will suffer from low illumination and not all of the image band will be visible (i.e., a loss of information). Furthermore, a narrowly focused lens sheet will need to be precisely positioned in relation to the composite image, which requires a rigorous manufacturing process, because of the distinct focal length of the lenses. The effective viewing distance for a display device having a narrowly focused lens sheet will also be limited to a small range.
Accordingly, there is a need for a process of manufacturing lenticular lens sheets that is simple and inexpensive and capable of forming lenticular sheets of virtually any size or shape. There is also a need for a lenticular lens sheet that, when used in a multiple image display device, provides brighter, clearer images that do not have a washed out appearance, that presents more information than conventional lens sheets, and that has a wide focusing tolerance.